The short answer
Quick answer
Most of the time, no. The majority of rigid-core luxury vinyl plank sold today comes with a pad already attached to the back, and when it does, you should not add a second one. You do need a separate underlayment in two cases: when your plank has no attached pad, and when you are installing over a concrete slab, where a 6-mil moisture barrier is a must. Over a wood subfloor, a plank with an attached pad goes down bare. The real decider is not "more foam." It is your subfloor and your plank. Get those two facts right and the answer is usually simple.
This is one of the most confused topics in flooring, and the internet makes it worse. Search it and you get a store trying to sell you underlayment, or a forum thread where one person swears you need a plastic sheet or your floor will collapse and the next says plastic under vinyl is useless. Both are half-right, which is the problem. After 20-plus years installing floors across Alexandria, Arlington, Fairfax, and the rest of the DMV, here is the version that actually answers your house.
First: does your plank already have a pad?
Quick answer
Flip a plank over and look at the back. If there is a soft foam or cork layer bonded to it, it has attached underlayment (usually labeled IXPE, EVA, or cork). Most rigid-core SPC and WPC planks do. If your plank has this pad, you do not add another one over a wood subfloor. If the back is bare rigid core, you need a separate underlayment.
This is the first question, and it settles most cases before you ever think about the subfloor. Manufacturers build the pad into the plank now because it is simpler and it protects the click joint. So before you buy a roll of anything, check the product. The spec sheet will say "attached pad" or "IXPE backing" if it has one. If your rigid-core plank already carries that pad, your floating floor is designed to go down on a clean, flat, dry subfloor with nothing extra between them. Adding a second layer is not a bonus. It works against the floor, which we get to below. If you are still choosing a plank, our WPC vs SPC guide covers which core you want.
When you do need underlayment
Quick answer
You need a separate underlayment when your plank has no attached pad, when you are floating over a concrete slab (for the moisture barrier), or when a condo or HOA requires a rated sound layer. In those cases the underlayment does a real job: cushion for a bare plank, a vapor barrier over concrete, or sound control between floors. Outside those three cases, it is usually optional or unwanted.
There are three honest reasons to roll out underlayment. One, your plank is bare-backed rigid core, so it needs a thin, dense foam pad to quiet the floor and fill the tiny gap under a floating install. Two, you are going over concrete, where the pad's job is moisture, not comfort. Three, you live in a condo or townhouse where the building requires a sound-rated layer under any hard floor. Each of those is a specific problem the underlayment solves. If none of them apply to your job, you probably do not need it.
When you can skip it
Quick answer
Skip separate underlayment when your rigid-core plank has an attached pad and you are floating it over a flat, dry wood subfloor. Also skip it entirely for glue-down and loose-lay vinyl, which are not designed to have anything soft underneath. In those cases, adding underlayment does nothing good and can cause problems.
The most common DMV job, a rigid-core plank with an attached pad going over the plywood subfloor of a bedroom or upstairs hallway, needs no separate underlayment at all. The pad is built in and the subfloor is wood, so there is no moisture issue to solve. Glue-down and loose-lay vinyl are their own case: they are meant to sit flat and bonded, so an underlayment under them is wrong by design. We cover the floating-vs-glue question in our glue-down vs floating LVP guide, because the install method changes this answer completely.
💡 Key takeaway
Underlayment is not a quality upgrade you add to make any floor better. It is a fix for a specific condition: a bare plank, a concrete slab, or a sound requirement. If you do not have one of those conditions, the best underlayment is often none.
Over concrete: the moisture rule
Quick answer
Over a concrete slab, always use a moisture barrier, even with an attached-pad plank. Concrete releases water vapor for its entire life, and that vapor has to be stopped before it reaches the floor. A 6-mil poly sheet, or an underlayment with a built-in vapor barrier, does that job. This is the one place the "plastic sheet" advice is actually right.
This is where the internet fight comes from, and both sides are missing the context. Over a wood subfloor, a plastic sheet under LVP does nothing, so the "you don't need plastic" crowd is right. Over concrete, that same sheet is doing critical work stopping vapor, so the "you must have plastic" crowd is right too. The answer is the subfloor. In the DMV that matters a lot, because basements, and most condos and ground floors on slab, are concrete. On any of those, we put a 6-mil vapor barrier down first, taped at the seams, then the floor. Skip it over concrete and you can get moisture, cupping, and mold under a "waterproof" floor. Our basement flooring guide walks through the slab-specific setup.
⚠️ Watch out
"My plank is waterproof, so I don't need a vapor barrier over concrete" is the mistake we see most. The plank is waterproof. The vapor still passes through the seams and sits underneath, where it has nothing to do but cause trouble. Waterproof plank and a sealed slab are two different protections. You want both.
Why doubling up backfires
Quick answer
Adding a second underlayment under an attached-pad plank makes the floor too soft. That extra flex stresses the click-lock joints as you walk, and over time the seams can separate, gap, or crack. It also usually voids the manufacturer's warranty, which specifically limits total pad thickness. More cushion feels like a good idea and is one of the fastest ways to break a vinyl floor.
People assume soft underfoot equals better, so they add a pad to a plank that already has one. It backfires. Rigid-core LVP locks together with a precise click joint, and that joint is engineered for a specific amount of give. Put too much foam under it and every step lets the floor deflect, which pries at the seams. The result is gaps, peaking, or a cracked locking edge months later. It is also written into most warranties: exceed the allowed pad thickness and the coverage is gone. This is why "just add underlayment to be safe" is bad advice for an attached-pad floor. The safe move is following the plank's spec, not stacking cushion.
Underlayment for sound (condos and townhouses)
Quick answer
If you are in a DMV condo or a stacked townhouse, your building may require a sound-rated underlayment under any hard floor, with a minimum IIC or STC number in the bylaws. This is a real rule, not a suggestion, and it is checked. In that case you use the specific rated underlayment the association requires, which can override the "attached pad is enough" answer.
Sound is the one place a condo owner genuinely needs to add underlayment, and it is not about comfort. Many DMV buildings, especially in Arlington, Tysons, and DC, require a rated acoustic layer under LVP so your footsteps do not carry to the unit below. The bylaws will name a minimum rating. When that rule applies, we use the required rated underlayment even under an attached-pad plank, because passing the building's spec comes first and the product is chosen to work as a system. If you are in a shared-wall home, read our soundproof flooring for condos and townhomes guide before you buy anything.
What we actually use
Quick answer
We match the underlayment to the job: nothing extra under an attached-pad plank on wood, a 6-mil vapor barrier or vapor-barrier underlayment over concrete, a thin dense LVP-specific pad under a bare plank, and the building-required rated layer in a condo. We do not use thick laminate underlayment under vinyl. And the right underlayment or moisture barrier is already included in our all-in price.
There is no single "best underlayment." The right one is the one your situation calls for, and using the wrong one is worse than using none. The most common mistake we fix is thick, spongy laminate underlayment installed under vinyl, which is the exact over-cushion problem from above. For vinyl we use a thin, dense pad only when the plank needs one, and a proper vapor barrier over concrete every time. This is part of why our pricing is all-in: at $5.50 a square foot for LVP, the correct underlayment and moisture barrier for your subfloor are already in the number, along with tearing out and hauling away the old floor. Our vinyl plank installation cost guide breaks down what that per-foot price covers.
The thing that matters more than underlayment
Quick answer
A flat subfloor matters far more than any underlayment. Rigid-core LVP needs the subfloor flat to within about 3/16 of an inch over 10 feet. Underlayment does not fix an uneven floor, it just drapes over the humps and hollows and lets the planks flex and click apart. If your subfloor is wavy, the fix is leveling, not a thicker pad.
Here is what people spend the least time on and should spend the most: how flat the subfloor is. LVP is thin and rigid, so it telegraphs every dip and rise underneath. No underlayment cures that. Roll a soft pad over a wavy floor and the planks still bridge the low spots, flex when you step, and eventually gap or crack at the seams. That is why we check flatness first and level where needed with patch or self-leveler before anything goes down. Older DMV homes especially, the 1950s colonials and Cape Cods, rarely have a dead-flat subfloor. Our guides on floor leveling cost and what we find under DMV floors cover the prep that actually makes a vinyl floor last.
FAQs about vinyl plank underlayment
Do you need underlayment for vinyl plank flooring?
Usually not. Most rigid-core LVP has a pad already attached, and when it does, you install it directly on a flat, dry wood subfloor with no separate underlayment. You do need one if your plank is bare-backed, if you are over a concrete slab (for the moisture barrier), or if your condo requires a rated sound layer. The subfloor and the plank decide it.
What happens if you don't use underlayment when you need it?
Over concrete with no vapor barrier, moisture can pass up through the slab and sit under the floor, leading to cupping, adhesive failure, or mold. Under a bare-backed plank with nothing, the floor sounds hollow and loud and the seams take more stress. Where underlayment is genuinely needed, skipping it shortens the floor's life. Where it is not needed, skipping it is correct.
Can you put underlayment under vinyl plank that already has a pad?
No, not over a wood subfloor. Doubling the cushion makes the floor too soft, which stresses the click-lock joints and can gap or crack the seams, and it usually voids the warranty. The only exception is a required vapor barrier over concrete or a building-mandated sound layer, which are chosen to work with the attached pad, not to add comfort.
Do you need underlayment for vinyl plank over concrete?
You need a moisture barrier, yes. Concrete gives off water vapor for its whole life, so a 6-mil poly sheet or a vapor-barrier underlayment goes down first, even under an attached-pad plank. This is the one case where the "always use plastic" advice is right. Over a wood subfloor, that same plastic sheet does nothing.
Is thicker underlayment better for vinyl plank?
No. Thicker is one of the most common causes of vinyl floor failure. Rigid-core planks need a thin, dense pad, not a soft spongy one. Too much give under the floor flexes the joints apart. If you want a quieter, more solid floor, the answer is a flat subfloor and the correct thin pad, not a thick one.
Does the underlayment go over concrete before or under the moisture barrier?
The moisture barrier goes down first, directly on the concrete, with seams taped, then any pad or the plank goes on top. The barrier's job is to keep slab vapor from ever reaching the floor, so it has to be the bottom layer. Many products combine the pad and vapor barrier into one sheet, which is fine over concrete.
Bottom line
Do you need underlayment for vinyl plank flooring? Usually not, if your plank has an attached pad and you are over a flat, dry wood subfloor. You do need it in three specific cases: a bare-backed plank, a concrete slab (where a moisture barrier is a must), or a condo with a sound rule. And you should not double up on an attached-pad floor, because more cushion breaks the seams and voids the warranty. The two things that actually make a vinyl floor last are matching the underlayment to the real condition and starting with a flat subfloor. We handle both, and the correct underlayment and moisture barrier for your house are already in our all-in $5.50 a square foot. Want it done right in Alexandria, Arlington, Fairfax, or anywhere in the DMV? Get a free in-home quote and we will check your subfloor and give you one honest price.